The present invention relates to a touch-panel input device overlayed on a liquid crystal panel, CRT or the like. An operator presses the device in a position corresponding to displayed information. The device determines the position pressed and sends appropriate command input data to a processing device such as a personal computer. The source of pressure on the device can be from a pen, finger or the like. More specifically, the present invention relates to a touch-panel input device that achieves improved visibility by sealing a transparent insulative fluid between transparent plates.
In general, touch-panel input devices are found on the display screen of a liquid crystal panel, CRT, or the like where an operator can select information by touching an appropriate area of the display. The touch-panel input device reacts to pressure applied to a transparent surface to indicate a specific position according to the contents of the display. The touch-panel device detects the display position selected and generates corresponding command input data. The generated command input data is then sent to a processing device such as a personal computer.
Touch-panel input devices of this type generally contain a movable plat positioned over a substrate. The substrate and movable plate are constructed to maintain a gap between the movable plate and the substrate when they are overlayed. The substrate and movable plate have conductive layers on the surfaces that face each other across the insulative gap. The conductive layers are made from transparent materials to provide visual access to the display screen. However, the presence of air between the substrate and the movable plate creates a large refraction index differential. This large refraction index differential results in a transmittance efficiency of 80%, making the screen difficult to view.
The difficulty in viewing the display screen is addressed in touch-panel input devices such as in Japanese laid-open patent publication number 64-14630 and Japanese laid-open patent publication number 2-105916. These publications disclose a solution to the above difficulty by injecting a transparent, insulative fluid between the substrate and the movable plate. The fluid has a refraction index that is close to that of the materials used in the substrate and the movable plate, thus reducing reflectivity and improving transmittance.
Referring to FIG. 4 and FIG. 5, there is shown a conventional touch-panel input device 100. A thin transparent plate 101 is a movable plate and transparent substrate 102 is a thick substrate that faces a display device (not shown). A frame-shaped spacer 105 is layered between transparent plate 101 and transparent substrate 102 to form a slight gap.
Transparent conductor layers 103, 104 are composed of an Indium Tin Oxide (ITO) film or the like, printed on the facing surfaces of transparent plate 101 and transparent substrate 102. The ITO film is printed on the facing surfaces with a uniform thickness. Leads 103a, 103b, 104a and 104b are also printed on these facing surfaces to provide electrical connections for transparent conductor layers 103, 104. A voltage generated at a contact point between transparent conductor layers 103, 104 is measured on the electrical path provided by leads 103a, 103b, 104a and 104b. The measured voltage at the contact point enables detection of the position at which transparent plate 101 is pressed.
Transparent conductor layers 103, 104 are usually separated by spacer 105. Dot spacers 106 are printed on transparent conductor layer 104 at regular intervals sufficient to prevent light pressure applied to transparent plate 101 from causing accidental contact between the transparent conductor layers 103, 104. Dot spacers 106 are composed of an insulative composite resin such as epoxy resin. Dot spacers 106 augment the gap separation provided by spacer 105 to prevent position from being detected when transparent plate 101 is accidentally or lightly touched.
Spacer 105 is composed of a tacking agent 105b applied to upper and lower surfaces of a thin plate 105a. A sealed space between transparent conductor layers 103, 104 and within spacer 105 is formed by tacking thin plate 105a to transparent plate 101 and transparent substrate 102. Thin plate 105a is tacked to transparent plate 101 and transparent substrate 102 at the perimeters of transparent conductor layers 103, 104.
Transparent plate 101 can move horizontally (in the direction indicated by the arrow in FIG. 5) over tacking agent 105b while maintaining a sealed space between transparent conductor layers 103, 104. This configuration provides a close, tight contact between transparent plate 101 and spacer 105, while at the same time permitting transparent plate 101 to move elastically over thin plate 105a in a horizontal direction. When pressure is applied to transparent plate 101, the region surrounding the point of contact is uniformly flexed toward transparent substrate 102. The flexure of transparent plate 101 remains uniform, even if the point of contact is near spacer 105 in a perimeter region of transparent plate 101.
Once a sealed space between transparent conductor layers 103, 104 is achieved, a transparent insulative fluid 107 is injected into the space. Transparent insulative fluid 107 has a refraction index that is relatively close to the refraction indices for the transparent conductor layers 103, 104. For example, ITO has a refraction index of 1.9, while silicon oil, an example of a transparent insulative fluid 107, has a refraction index of 1.4.
Interposing transparent insulative fluid 107 between transparent conductor layers 103, 104 reduces the amount of light reflected by touch-panel input device 100 when exposed to an illumination source (not shown) located above touch-panel input device 100. Since transparent insulative fluid 107 has a refraction index relatively close to that of transparent conductor layers 103, 104, overall light transmittance increases to around 90%. The light reflected by touch-panel input device 100 is correspondingly reduced, thus significantly improving visibility of the display screen.
In this conventional touch-panel input device 100, spacer 105 determines the width of the gap between transparent conductor layers 103, 104. The width of the gap is therefore determined by tacking agent 105b and frame-shaped thin plate 105a, which make up spacer 105. The width of the gap is determined when tacking agent 105b is applied to upper and lower surfaces of thin plate 105a. This gap is generally in the range of from 60 to 300 microns.
When the device is operated, pressure applied to transparent plate 101 displaces transparent insulative fluid 107 and contact is made between transparent conductor layers 103, 104. Generally, a large amount of transparent insulative fluid 107 is interposed between transparent conductor layers 103, 104. Therefore, excessive pressure is required to close the gap of from 60 to 300 microns and cause transparent conductive layers 103, 104 to contact each other.
Moreover, when the applied pressure is released, transparent plate 101 is not restored to its original position immediately. A large amount of transparent insulative fluid 107 must return to the point of contact between the transparent conductor layers 103, 104 before transparent plate 101 is completely restored to its original position. The requirement for flow of a large volume of transparent insulative fluid 107 to the contact point makes restoration of the position of transparent plate 101 slow. This slow restoration makes the touch-panel input device 100 and screen combination difficult to use. Problems attendant with the use of the combination include such difficulties as, for example, slow responsiveness and lingering Newton rings on the operating surface caused by light interference.
In addition, a vacuum cavity is produced in an upper section of touch-panel input device 100 when the device is tilted. The vacuum cavity is produced due to the large gap between transparent conductor layers 103, 104 which permits the weight of transparent insulative fluid 107 to overcome surface tension when the device is tilted. The resultant vacuum cavity causes reduced light transmittance and malfunctions in the device.
Furthermore, touch-panel input device 100 can be configured for use as an input device in a mounted vehicle navigation system. The demands of such an application require the device to function in environments of 70 degrees Celsius or higher. The relatively large gap between transparent conductor layers 103, 104 provides the capacity for a large quantity of transparent insulative fluid 107 to be interposed therebetween. When this relatively large quantity of transparent insulative fluid 107 is warmed to environmental temperatures, it experiences thermal expansion. Escape openings must be provided for transparent insulative fluid 107 to expand in the sealed space without damaging touch-panel input device 100. Such escape openings communicate between the sealed space and an external environment of the device. Providing such escape openings, however, creates the additional problem of transparent insulative fluid 107 leaking from the device and becoming oxidized upon contact with external air.
The above described problems could be overcome by narrowing the gap between the transparent conductor layers 103, 104, thus reducing the capacity of the space therebetween for containing transparent insulative fluid. However, utilizing spacer 105 to provide such a narrow gap construction limits the gap width to greater than 50 microns. A more desirable, narrower gap is not possible according to the construction of spacer 105 when formed by applying tacking agent 105b to both sides of thin plate 105a. 
Moreover, tacking agent 105b is formed by dissolving a tacky binder in a solvent. The use of the solvent creates the possibility of the solvent dissolving into transparent insulative fluid 107. Such a dissolution of solvent in transparent insulative fluid 107 adversely affects the transparency and insulative properties thereof.
Alternatively, spacer 105 can be replaced with a reactive adhesive used to bind transparent plate 101 and transparent substrate 102. Such a construction produces a gap between transparent conductive layers 103, 104 corresponding to the height of the adhesive layer. Using such a construction technique, the height of the adhesive layer can be suitably modified to reduce the width of the gap.
However, application of the above described reactive adhesive to the touch-panel device 100 causes transparent plate 101 to be rigidly fixed to transparent plate 102. When the two plates are fixed in such a manner as described, the configuration prevents elastic horizontal movement of transparent plate 101. Pressure applied to transparent plate 101 near the adhesive layer in the above described configuration causes transparent plate 101 to be pulled toward the adhesive layer. Transparent plate 101 lapses into a position in which it tilts significantly. This problem can result in detection errors due to discrepancies in the position being pressed and that which is actually sensed. Detection errors can also occur if the transparent conductor layer 103 fails to reach the transparent conductor layer 104 upon the application of external pressure.
Various technologies have been proposed to deal with the above drawbacks in a touch-panel input device. However, no adequate technology has been found to overcome the above described difficulties which can be easily implemented. Generally, solutions to the problem of sealing a transparent insulative fluid in a gap to improve transmittance have been extremely difficult to implement.
In view of the above discussion, it is an object of the present invention to overcome the drawbacks of the prior art.
It is also an object of the present invention to provide a touch-panel input device that reduces the gap between the conductor layers.
It is a further object of the present invention to provide a touch-panel input device that offers reliable detection of positions indicated by pressure.
It is still another object of the present invention to provide a touch-panel input device with a uniform operational tactile response, even when pressure is applied to an area near a corner or side of the input device.
A still further object of the present invention is to provide a touch-panel input device that offers reduced reflectivity, improved transmittance, quick responsiveness and uniform transmittance, even when the device is tilted.
Briefly stated, two transparent conductive panels are separated by a perimeter of elastic adhesive that forms a sealed gap in which transparent insulative fluid is interposed. The fluid has a refraction index close to that of the panels to improve light transmittance through the device. The small width of the gap improves response time and prevents formation of a vacuum in the gap. The panels are connected to a position detection circuit that determines coordinate position of an applied pressure point. Spacers in the gap reduce the chance of accidental large-area contact which would result in an erroneous position command. The elasticity of the adhesive and the small gap width provide better temperature variation tolerance in addition to improved consistency and reliability of operation.
According to an embodiment of the present invention, there is provided a touch-panel input device comprising: at least first and second transparent plates having faces opposed to one another and substantially parallel, a portion of said opposing faces of said at least first and second transparent plates being transparent electrically conductive surfaces with uniform surface resistance, an elastic adhesive disposed around a perimeter of said conductive surfaces, whereby said opposing faces are bonded together and separated by a sealed gap having a uniform width, a transparent insulative fluid interposed in said sealed gap, said fluid having a refraction index close to that of said transparent plates, at least one of said at least first and second transparent plates capable of resiliently flexing toward an other of said transparent plates, whereby an electrical relationship is changed between said conductive surfaces and said relationship is related to a coordinate position on said device.
According to a method of the present invention there is provided a method for constructing a touch-panel input device comprising steps of: forming transparent conductive layers with conductive leads on portions of at least two transparent plates, disposing a curable reactive adhesive on a perimeter of one of said conductive layers, curing said reactive adhesive to form an elastic pressure sensitive adhesive with a specified height above said transparent plate, applying a conductive bonding agent to an external connector, positioning said external connector in a region outside of a space defined by said adhesive and in contact with said conductive leads, pressing said transparent plates together with said conductive layers being opposed thereby bonding said transparent plates together and forming a sealed gap between said conductive layers and interposing an insulative transparent fluid in said gap, said fluid having a refraction index near that of said transparent plates.
According to another embodiment of the present invention there is provided a touch-panel input device comprising: at least first and second transparent plates having faces opposed to one another and substantially parallel, transparent electrically conductive layers disposed on each of said opposing faces, said conductive layers having substantially uniform surface resistance and transparent electrical connection leads disposed on opposing ends of said conductive layers, pairs of said connection leads of said conductive layers defining a coordinate axis, regularly spaced insulative protrusions on at least one of said conductive layers effective to slightly increase and evenly distribute pressure applied to said transparent plates needed to cause contact between said conductive layers, an elastic adhesive disposed around a perimeter of said conductive layers, whereby said opposing faces are bonded together and separated by a sealed gap having a substantially uniform width, transparent insulative fluid interposed in said sealed gap, said fluid having a refraction index close to that of said transparent plates and an external connector connected to said leads.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.